German pharmaceutical company Merck KGaA (MRK.XE) shares rose Wednesday after the company said an independent study showed colon cancer patients lived three and a half months longer when its Erbitux drug was added to their treatment.

The study showed patients with a specific genetic makeup who received a combination of Erbitux and chemotherapy lived a median of 23.5 months compared with 20 months for patients on chemotherapy alone.

At 0927 GMT, Merck shares were up EUR1.78 or 2.6% at EUR70.66, outpacing a 0.5% rise in the DAX.

The results were presented Wednesday at the European Society for Medical Oncology congress in Berlin.

Erbitux, a monoclonal antibody whose active ingredient is called cetuximab, is already approved as a primary treatment in combination with chemotherapy for colon cancer. Analysts consider the drug a potential blockbuster, with peak annual sales of at least EUR1 billion. It is marketed in the U.S. by Eli Lilly & Co. (LLY) and Bristol-Myers Squibb Co.(BMY).

The drug competes with Amgen Inc.'s (AMGN) Vectibix for a group of colon cancer patients who carry a normal form of a gene called KRAS. Studies show patients who have a mutated form of the gene - about a third of all colon cancer patients - don't respond to Vectibix or Erbitux. In July, the U.S. Food and Drug Administration revised the labels on the drugs to recommend that they not be used to treat patients with the genetic mutation.

The data presented Wednesday focused on patients with the normal KRAS gene.

On Thursday, Amgen is expected to present data on the effectiveness of Vectibix as a primary colon cancer treatment in combination with chemotherapy for normal KRAS patients. If approved as a primary treatment, Vectibix would likely snare some of Merck's market share.

On Tuesday, data was presented showing patients who took Vectibix as a secondary treatment lived two months longer than those on chemotherapy alone. However, the data isn't considered statistically significant.

Commerzbank analyst Daniel Wendorff said Vectibix doesn't pose much of a threat to Erbitux based on the data presented so far. He still sees Erbitux garnering EUR692 million in sales in 2009 and EUR1 billion in 2013.

-By Allison Connolly, Frankfurt Bureau; +49 69 29725513, allison.connolly@dowjones.com